In one known hook system, a bobbin case assembly and bobbin basket assembly cooperatively define a receptacle for a bobbin and are fully separable, each from the other. The bobbin basket assembly and bobbin case assembly are operatively connected to a hook assembly having an operating axis. The bobbin basket assembly has a peripheral wall with a radially outwardly projecting bearing rib thereon which is guided in a complementary raceway defined by the hook assembly. In operation, the hook assembly is rotated at high speed. Ideally, the bearing rib rides smoothly within the raceway at these high speeds.
It is known to make both the bobbin basket assembly and bobbin case assembly from metal to maximize durability and minimize wear. At high operating speeds, friction may be generated between the metal bobbin basket assembly and hook assembly that generates heat sufficient to cause part expansion that may result in binding of the bearing rib on the bobbin basket assembly within the raceway of the hook assembly.
Further, if there is improper alignment between the bobbin basket assembly and hook assembly, or the hook assembly is out of dynamic balance, damage may be inflicted, one to the other, by the bobbin basket assembly and hook assembly.
To address, among other things, the above problems, the inventor herein devised rotary hook systems with non-metallic bobbin basket assemblies. This has resulted in a substantial weight reduction which has contributed to overall improved sewing performance. However, to the knowledge of the inventor herein, bobbin case assemblies are, to this day, made primarily from metal. The metal bobbin case assembly has a sufficient weight that it potentially detracts from performance.
Further, the metal case assembly does not lend itself to being formed into intricate shapes in an economical manner.
The above problems are contended with both in systems which use a hook assembly that rotates continuously in one direction and those which use an oscillating hook assembly.